Thermo-piezoresistive embedded wireless sensor with real-time concrete monitoring

ABSTRACT

Embodiments are described herein for a sensor device created for determining and monitoring quality and strength developments in concrete and other materials using temperature and electrical resistivity parameters. The embodiments described herein may be utilized in the construction industry for real-time monitoring of concrete and cement structures or for monitoring the strength and quality of soils, polymers, and liquid additives as well. According to various embodiments, alternating current (AC) electrical and temperature measurements may be performed to correlate to the quality and performance of the concrete, polymers, treated soils, and other materials. These measurements may be made by compact sensor devices that are configured to read both temperature and AC electrical measurements continuously to quantify the performance of materials.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalPatent Application No. 63/054,283 filed Jul. 21, 2020, entitled“THERMO-PIEZORESISTIVE EMBEDDED WIRELESS SENSOR WITH REAL-TIME CONCRETEMONITORING,” the contents of which being incorporated by reference intheir entirety herein.

BACKGROUND

Cement and concrete are used worldwide in a variety of constructionprojects, from small to large residential homes to even massivecommercial structures. Because of this large consumption of concrete,new techniques and methods of quality control have arisen. Concrete is aunique building material that can withstand both fire and water, amongothers. Because of this unique quality, it is the most widely usedbuilding material in the world. Additionally, concrete is one of theoldest known man-made materials and currently about ten billion tons ofconcrete are produced every year.

Due to the rapid development of more demanding concrete infrastructuresworldwide, a variety of concrete types are currently available whichinclude high strength concrete, high density concrete, high sulphateresistant concrete, lightweight concrete, quick setting concrete, and soon. These different variations in concrete are achieved by mix ofvarious admixtures, changing aggregates, water to cement ratios, andother parameters. Admixtures are also used to modify the hydrationprocess of concrete to slow down or speed up the hydration process. Someadmixtures are added into the concrete mixtures to obtain highercompressive strength, durability, and/or to improve the workability. Dueto such high variation in requirements, it is important to monitor thestrength and quality of concrete continuously. Real-time monitoring forconcrete is a revolutionary approach because it allows the end user tomake more quick and informed decisions during and after the placement ofthe concrete.

Structures rely on concrete as a construction agent due to itscompressive strength, durability, and cost efficiency. Concrete is aheterogeneous material that consist of a mixture of water, cement, fineaggregates, coarse aggregates, fiber/steel, and different otheradmixtures which makes it very sensitive during the curing process.During this process, concrete gains close to 90-95% of its compressivestrength in twenty-eight days of curing and about 3-5% increase whencured up to six months.

Concrete is believed to gain strength over time even after six months,but it is crucial to quantify and monitor the strength of concreteduring and after the 28 days period, as it reaches close to 90 to 95%strength. There are several techniques used to monitor the curingprocess of fresh concrete nowadays, but without accurate and continuousmonitoring, these techniques are not enough for attaining real-time dataon concrete strength developments. Thus, concrete needs to be monitoredprecisely from right after it is poured until the twenty-eighth day todetermine whether it has achieved the specified design strength. For anyconcrete mix, it is necessary to monitor the strength development at anearly age because changes in the environment such as temperature andcold weather can affect the curing process of fresh concrete. The mainpurpose of quality control methods is to prevent catastrophes andpreserve human lives, ensure best construction practices, and expeditethe construction processes while cutting costs.

BRIEF SUMMARY OF THE INVENTION

Embodiments are described herein for a wireless sensor created forrecording, monitoring, and characterizing quality and strengthdevelopments in concrete using temperature and electrical methods. Insome embodiments, the concrete is “fresh concrete,” or, in other words,recently-poured concrete. The embodiments described herein may beutilized in the construction industry for real-time monitoring ofconcrete and other cementitious materials for continuouscharacterization. The embodiments described herein may also be utilizedfor monitoring the strength and quality of soils, polymers, solutions,and liquid additives as well. In accordance with an embodiment of theinvention, a method is described that comprises performing electricalimpedance measurements inside concrete in real time for both wet andhardened conditions in laboratory and field applications. According tovarious embodiments, alternating current (AC) electrical and temperaturemeasurements may be performed to correlate to the quality andperformance of the concrete, polymers, treated soils, solutions, andother cementitious materials. These measurements may be made by compactwireless sensors configured to read both temperature and AC electricalmeasurements continuously to quantify the performance of materials.

In accordance with an embodiment of the invention, a method is providedfor AC electrical impedance measurement inside cementitious materialsand determining at least one characteristic of concrete, wheretemperature and/or geometrical factor correction are employed.Determining the characteristic of concrete may include, for example, atleast one of the following: determining quality control parameters, suchas water cement ratio, contaminations, setting times, and temperature;determining pore solution properties, such as electrical conductivity,transport properties, such as permeability, porosity, and diffusivity;determining durability characteristics, such as voids, cracking,corrosion, or any damage to the materials; determining performancecharacteristics, such as compressive strength and slump.

In accordance with embodiment of the invention, a method is providedcomprising performing temperature and/or electrical impedancemeasurements in wet and/or solid (or hardened) cementious materials inlaboratory and/or field settings in real time; transmitting thetemperature and impedance measurements to a remote computing device(e.g., a server) for processing characteristics of cementitiousmaterials; and communicating the characteristics of cementitiousmaterials to a computing device associated with an enterprise. Inaccordance with an embodiment of the invention, a method for reuse ofsensor with replaceable probe component is described.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, with emphasis instead being placed uponclearly illustrating the principles of the disclosure. Furthercharacteristics, features, and benefits of the embodiments describedherein will become evident after the clarification of the detailedillustration of figures.

FIG. 1 is a perspective view of a sensor device for real-time concretemonitoring according to various embodiments of the present disclosure.

FIG. 2 is another perspective view of the sensor device according tovarious embodiments of the present disclosure.

FIG. 3 is a waterproof electrical connector for precast applicationsaccording to various embodiments of the present disclosure.

FIG. 4A is a copper electrode according to various embodiments of thepresent disclosure.

FIG. 4B is a plastic mixing arm according to various embodiments of thepresent disclosure.

FIG. 4C is a porous plastic filter according to various embodiments ofthe present disclosure.

FIG. 5 is an interior layout of a printed circuit board (PCB) and acorresponding components list and description table according to variousembodiments of the present disclosure.

FIG. 6 is an example of an installation process for installing a sensorin concrete formwork according to various embodiments of the presentdisclosure.

FIG. 7 is an example of pouring concrete after placement of a sensor inconcrete formwork according to various embodiments of the presentdisclosure.

FIG. 8 is an example of communicating wirelessly with a sensor accordingto various embodiments of the present disclosure.

FIG. 9 is a temperature plot showing temperature of concrete versus timeaccording to various embodiments of the present disclosure.

FIG. 10 is a maturity plot showing maturity from temperature versus timeaccording to various embodiments of the present disclosure.

FIG. 11 is a compressive strength plot showing compressive strength ofconcrete versus time according to various embodiments of the presentdisclosure.

FIG. 12 is an electrical resistivity plot showing electrical resistivityversus time according to various embodiments of the present disclosure.

FIG. 13 is a compressive strength using electrical resistivity plotshowing compressive strength of concrete versus time according tovarious embodiments of the present disclosure.

FIG. 14 is an equivalent circuit diagram illustrating a total impedanceof a sensor device embedded in concrete or other material according tovarious embodiments of the present disclosure.

FIG. 15 is a plot of impedance versus frequency of a circuit accordingto various embodiments of the present disclosure.

FIG. 16 is a schematic diagram that represents two independent testingparameters that portray a substantially linear relationship betweenelectrical resistance and electrical resistivity.

FIG. 17 is a plot illustrating a linear relationship between electricalresistance and electrical resistivity according to various embodimentsof the present disclosure.

FIG. 18 is a plot of electrical resistance versus electrical resistivityfor concrete according to various embodiments of the present disclosure.

FIG. 19 is a plot of a K-value for concrete versus time according tovarious embodiments of the present disclosure.

FIG. 20 is a plot showing a resistivity versus time curve according tovarious embodiments of the present disclosure.

FIG. 21 is a plot showing a resistivity time factor according to variousembodiments of the present disclosure.

FIG. 22 is a table showing a cumulative resistivity time factor versuscompressive strength according to various embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The present disclosure relates to a thermo-piezoresistive embeddedwireless sensor with real-time concrete monitoring. Concrete materialtesting methods currently require concrete samples or “cylinders” to becollected from job sites for each of the concrete mix-designs used in aproject. The samples are then carefully transported to a MaterialsTesting Lab (MTL) for testing. Typically, the MTL lets each concretecylinder “specimen” cure for about three, seven, fourteen, ortwenty-eight days before performing testing. Sequentially, after eachconcrete specimen is fully cured, the MTL performs a compressivestrength test which includes performing various measurements by breakingeach concrete cylinder in a compression-testing machine to determine atwhat pound-force per square inch (PSI) each concrete cylinder breaks.This assumes that the sample has not be broken during collection and/ortransport.

The test results are sent to construction owners to inform the owners ofthe PSI of each concrete specimen, which is correlated to the PSI forconcrete poured in the field. However, these testing methods have beenaround for decades and they do not provide the necessary information inreal-time for construction owners, general contractors, suppliers,regulators, architects, and civil engineers to make quick and moreinformed decisions about the performance and quality of concrete.Currently, the seven days lead time that MTL takes before sendingresults back to the end user is a hurdle to the construction industrywhere time is money.

Establishing rapid real-time testing of concrete quality and strength isthe current aspect of interest. The use of thermocouples and sensors fortemperature measurement in concrete to predict the strength are alsoaccepted in the building standards for construction. Nonetheless,temperature measurements have proved to be accurate in controlledenvironment settings, but there are several limitations in applying thetechnology to the field. One limitation is the temperature beinginfluenced by the outside environment elements, such as hot and coldweather. Another limitation is that temperature measurements areaffected by the size and thickness of the structure being built, and thelocation where a sensor is placed may affect readings due to atemperature of concrete varying from place to place. Notably,temperature sensors cannot differentiate between void space and thepresence of concrete at the measurement location.

Furthermore, temperature measurements are not used solely for earlyconcrete strength predictions due to temperature not being a truematerial property of concrete. On the other hand, electrical resistivityof concrete is a material property and provides accurate correlation tohydration reaction of concrete. This parameter can be used to predict amuch more accurate strength predictions in fresh concrete. Estimation ofstrength and quality of concrete in real time using alternating currentelectrical resistivity measurements are described herein may providecontractors, owners, and others with highly accurate results, therebyreducing the dependence on break tests that are currently done, whichcause longer construction waiting time and are expensive.

More details and features of the embodiments described herein will bedescribed below. Specifically, the embodiments described herein addresslimitations within the current testing methods for concrete, cement,treated soils, solutions and polymers more particularly electricalmethods and systems. Further, the embodiments described herein mayutilize electrical impedance measurements to monitor the chemicalreaction in concrete, such as fresh concrete, to determine the strengthand quality thereof in real-time. The alternating current electricalimpedance measurement may be performed at high-frequencies and may beused to calculate electrical resistivity based on a correction togeometric factor K—temperature adjustment. The embodiments describedherein may provide electrical conductivity of pore solution insidecementitious materials in real time.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

Referring now to FIGS. 1 and 2, non-limiting examples of a sensor device100 are shown in accordance with various embodiments. The sensor device100 is configured to be embedded in concrete, dirt, or otherconstruction material while still being able to capture measurements ofthe construction material or properties thereof, and communicate themeasurements to a computing device outside of the construction material.

In some embodiments, the sensor device 100 includes an enclosure 103, awire 106, and one or more probes 109 a . . . 109 c (collectively “probes109”) extending from and/or partially nested in a probe housing 112,among other features and components as will be described. The enclosure103 may include an outer surface and a hollow interior, and may furtherinclude one or more projections 115 a, 115 b (collectively “projections115”) defining apertures or openings for insertion of zip-tie and/orwire-tie capability. For instance, the enclosure 103 of the sensordevice 100 may be bound to rebar or other desirable location usingzip-ties, wire ties, or other suitable connection mechanism via theapertures of the projections 115, as will be described.

Housed within the enclosure 105 of the sensor device 100 may becircuitry as well as additional components such as, for example, atemperature probe 118, a bulk material electrical resistivity probe 121,a pore solution electrical conductivity probe 124, and/or processingcircuitry 127. The processing circuitry 127 may include, for example, abattery 130 or other power source, a microprocessor 133, impedancemeasurement circuitry 136, temperature measurement circuitry 139, atransceiver 142 (or a transmitter), a power switch 145, memory 148(e.g., memory of the microprocessor 133 and/or a removable memory card),among other components as may be appreciated.

The impedance measurement circuitry 136 and/or the temperaturemeasurement circuitry 139 may be part of or communicatively coupled tothe processing circuitry 127, which includes a microprocessor 133 invarious embodiments. The impedance measurement circuitry 136, thetemperature measurement circuitry 139, and/or the processing circuitry127 may be communicatively coupled to the wire 106, which may include anelectrically conductive wire extending out of the enclosure 103 toconnect to one or more probes 109. The probes 109 may include, forexample a pair of electrical resistivity and electrical conductivityprobes 109 a, 109 b and a temperature probe 109 c in some embodiments,although other probes 109 may be employed. In some embodiments, theelectrical resistivity and electrical conductivity probes 109 a, 109 bmay be gold-coated, although other suitable materials may be employed.

As may be appreciated, the electrical resistivity and electricalconductivity probes 109 a, 109 b may be used for electrical impedancemeasurement as they have a standard predetermined geometric factor value(e.g., a K-value) to be utilized for bulk material electricalresistivity and electrical conductivity of pore solution calculations,or other types of calculations.

In some embodiments, the temperature and electrical resistivity probes109 a, 109 b may be connected using an electrical connector, such as afour pin waterproof electrical connector 150 to the sensor device 100shown in FIG. 3. This connector may assist in reuse of the sensor device100. For instance, the connector 150 of FIG. 3 may be used for precastconcrete applications with probes 109 that are disposable or reusable,such that the connector 150 is positioned at least partially external toprecast concrete. The connector 150 may couple to the wires 106, 152 ofFIG. 1 or 2.

While the embodiment of FIG. 1 shows various types of probes 109,additional types of probes may be employed. For instance, in FIG. 2, thesensor device 100 includes not only a first wire 106 that couples thehousing 103 and the components therein to a first probe arrangement 152(comprising the probes 109), the sensor device 100 further includes asecond wire 152 that couples the housing and the components therein to asecond probe arrangement 155.

In some embodiments, as shown in FIGS. 3A-3C, in order to monitor theelectrical conductivity of a pore solution, the second probe collection155 may include electrodes 158 (FIG. 3A), a plastic mixing arm 161 (FIG.3B), and a filter 164 (FIG. 3C) that is connected to the sensor device100. The electrode 158 may include copper electrodes, the mixing arm 161may include a plastic mixing arm, and/or the filter 164 may include aporous plastic filter in various embodiments. The filter 164 is notshown in FIGS. 3A and 3B for explanatory purposes. The working of theprobes inside the pore solution conductivity relies on the sameprinciples as that of electrical resistivity probe described herein.

Turning now to FIG. 5, FIG. 5 is an interior layout of a printed circuitboard (PCB) 167 that may be a part of the processing circuitry 127 isshown according to various embodiments of the present disclosure. InFIG. 5, the PCB 167 includes testpoints TP2, TP3, TPS, TP6, an antennaM1 (e.g., a Bluetooth chip antenna), diodes D2, D3 (e.g., TVS DIODE 5V12.3V SOD923), capacitor C14 (e.g., CAP CER 10UF 10V X7R 0805), resistorR14 (e.g., RES SMD 100K OHM), resistor R29 (e.g., RES SMD 100K OHM 1%/16W), capacitor C30 (e.g., CAP CER 01UF 25V X7R 0402), resistor R39 (e.g.,RES SMD 47K OHM 1%/16 W), a network analyzer U4 (e.g., IC networkanalyzer), capacitor C31 (e.g., CAP CER 0.1UF 25V X7R 0402),capacitor-resistor C6-R5 (e.g., CAP CER 01 UF 25V), capacitor C2 (e.g.,CAP CER 10PF 10% 25V NPO 0402), and/or other components not describedherein. The dimensions of al may include 38.00 mm, α₂ may include 38.00mm, and α₃ may include 6.00 mm, although other desirable dimensions maybe employed.

According to various embodiments described herein, the sensor device 100and the processing circuitry 127 thereof, and/or an external computingdevice in communication with the sensor device 100, may be configured todetermine initial and final setting times of concrete in a fieldcompared to laboratory calibration; verify water to cement ratio of wetconcrete and moisture content of solid concrete; determine in-situcompressive strength of concrete in real-time right from pouring througha twelve month period; make real-time predictions of compressiveconcrete strength and quality at predefined intervals (e.g., one-day,three-day, seven-day, twenty-eight-day, and fifty-six-day intervals)using electrical resistivity correlation; perform real-time detection ofvoids or soil contamination in wet concrete during and after theplacement of concrete; quantify the properties of concrete, such aspermeability, porosity, and diffusion using correlations to electricalresistivity measurements; quantify the pore solution electricalconductivity in concrete during and after placement; perform real-timedetection of cracks in concrete structures and trace development overtime; perform real-time determination of presence of chloride, sulphate,and/or other ions that affect the integrity and quality of concrete;determine the rate of corrosion of rebar inside the concrete using theabsolute value of electrical resistivity of concrete; determine anabsolute value of electrical resistivity from electrical impedancemeasurements and predicting the quality and strength parameters ofconcrete in real time for up to twelve months or other suitable periodof time; perform real-time temperature and alternating currentelectrical impedance measurements of concrete for a period of up totwelve months or other suitable period of time; transmit or otherwisecommunicate the absolute value of quality and strength parameters ofconcrete and the change in parameters over time; perform temperature andalternating current electrical impedance measurement in concrete at apredefined period of time (e.g., twelve months) from a pour of concrete;transmit or otherwise communicate the time, temperature, and electricalimpedance measurements to a remote server that processes the electricalimpedance data to calculate the value of electrical resistivity of theconcrete; determine quality and strength parameters of concrete; and/ortransmit or otherwise communicate the quality and strength parameters inreal-time to a predetermined enterprise to provide visualinterpretation.

Now, a non-limiting example of a method of use of the above-describedsensor is described. First, as shown in FIG. 6, a sensor device 100, asdescribed herein, may be turned on or otherwise enabled and placed ontoa concrete reinforcement structure 172, such as rebar. In order tomaximize wireless antenna range (e.g., the range of the transceiver142), the enclosure 103 and the components residing therein (e.g.,processing circuitry 127) may be placed at a predefined distance from asurface of the concrete or other material to be poured. In someembodiments, the predefined distance includes approximately three inches(7.5 cm) or other suitable distance.

The sensor device 100 may be tightened or otherwise adequately coupledto the concrete reinforcement structure 172 (e.g., rebar) to reduce therisk of the sensor device 100 being flipped over when the concrete ispoured. The transceiver 142 of the sensor device 100 (or other suitablereceiver and/or transmitter) may be kept in an upward position to enablea connection and communication between the sensor device 100 and anexternal computing device, such as a mobile computing device (e.g., asmartphone, laptop, tablet, etc.). In some embodiments, the connectionand communication is performed wirelessly although, in alternativeembodiments, a third wire (not shown) may be positioned in the concretesuch that the third wire projects from a cured surface of the concrete,allowing for a physical connecting between the third wire and one ormore computing devices.

Second, before pouring concrete, the wire 110 that connects theenclosure 105 (and the components therein) to the probes 115 may bepositioned under the concrete reinforcement structure 172 to protect itfrom potential damage. Then, it is ensured that temperature andresistivity probes 115 do not touch a ground or any other surface otherthan the fresh concrete mix. Finally, as shown in FIG. 5, the concreteis poured and cured, while the sensor device 100 starts collecting datawhich is stored in the memory 148 of the sensor device 100.

After the sensor has been properly installed and fresh concrete poured,a user can connect to the sensor using a computing device 175, forexample, to search for nearby sensor devices 100 using a clientapplication. In embodiment in which wireless communication is employed,the computing device 175 may pair with or otherwise connected to thesensor device 100 using the ZigBee® communication protocol, theBluetooth® communication protocol, or other suitable near fieldcommunication protocol.

In some embodiments, the sensor device 100 may transmit data up toforty-nine feet (fifteen meters) of distance between the location of thesensor device 100 and the computing device 175. However, other desirableranges may be employed. The frequency of the measurements can beadjusted to a desired time interval (e.g., every five minutes), and mayhave a life of the battery 130 (or a battery life) of six months afterinstallation in some embodiments. It is understood that increasing thetime between measurements may increase the life of the battery 130. Thesensor device 100 thus may provide real-time data measurements ontemperature, maturity, resistivity, and strength of concrete throughmetrics, graphs, or other data that may be rendered in a user interfaceto be shown in a display as well as, for example, a point and time whenthe data was recorded.

The data collected from the sensor device 100 may allow an individual tomake more informed decisions during and after the pouring of freshconcrete. For instance, a client application (executable on thecomputing device 175) may be configured to enable an end user to setthresholds for when the concrete has reached the desired strength,notably, without having to wait three to seven days before getting labresults. Alerts and notifications may inform the user when it is theappropriate time to remove formwork and other building assistanceequipment. Over time, all the data collected from the different concretemix-design and the data collected from the sensor embedded in the freshconcrete could have the potential to provide real-time feedback based onthe property of concrete use, job sites geographic location, andconcrete curing process.

Impedance Model for Electrical Property Characterization: EquivalentCircuit. FIG. 14 depicts a non-limiting example of an equivalent circuitthat represents electrical properties of a material (e.g., concrete) tocharacterize its performance with time. There are many difficultiesassociated with choosing a correct equivalent circuit. It is derisible,however, to connect the different elements in the circuit to differentregions in the impedance data of the corresponding sample. Given thedifficulties and uncertainties in establishing this connection,researchers tend to take a pragmatic approach and adopt a circuit whichthey believe to be most appropriate from their knowledge of the expectedbehavior of the material under study, and demonstrate that the resultsare consistent with the circuit used. With the sensor described herein,different possible equivalent circuits were analyzed to find anappropriate equivalent circuit to represent concrete, cementitiousmaterials, and polymers.

Special Bulk Material—Resistance Only. In the equivalent circuit, theelectrical contacts were connected in series, and both the electricalcontacts were represented using a capacitor C_(c) and a resistor R_(c)connected in parallel, as shown in FIG. 12. The bulk material wasrepresented by a resistor R_(b). In other words, in the equivalentcircuit, R_(b) is the resistance of the bulk material, and R_(c) andC_(c) are resistance and capacitance of the contacts, respectively. Bothcontacts are represented with the same resistance Rc and capacitance Ccin embodiments in which they are made in an identical manner and includeidentical materials. A total impedance of the equivalent circuit Z₁ canbe represented as shown in eq. 1 below.

$\begin{matrix}{{{Z_{1}(\sigma)} = {\frac{R_{b}(\sigma)}{1 + {\omega^{2}R_{b}^{2}C_{b}^{2}}} + \frac{2{R_{c}(\sigma)}}{1 + {\omega^{2}R_{c}^{2}C_{c}^{2}}} - {j\left\{ {\frac{2\omega R_{c}^{2}{C_{c}^{2}(\sigma)}}{1 + {\omega^{2}R_{c}^{2}C_{c}^{2}}} + \frac{2\omega R_{b}^{2}{C_{b}^{2}(\sigma)}}{1 + {\omega^{2}R_{b}^{2}C_{b}^{2}}}} \right\}}}}.} & \left( {{eq}.\mspace{14mu} 1} \right)\end{matrix}$

In this case, the capacitance of the bulk material, denoted C_(b), isassumed to be negligible, as can be seen in FIG. 15. When the frequencyof the applied signal is very low, ω→0, Z₂=R_(b)+2R_(c), and when it isvery high, ω→∞, Z₂=R_(b). The shape of the curves shown in the figure isvery much influenced by material response and the two probe instrumentsused for monitoring. Testing of concrete indicated that electricalimpedance represented their behavior and hence the bulk materialproperties can be represented by resistivity and characterized at afrequency of 100 kHz to 1 MHz using the two probes. The electricalresistance of material can be obtained by measuring impedance at high ACfrequencies and can be converted into electrical resistivity usingK-value as shown below.

The relation between electrical resistance, electrical resistivity andK-value is given by eq. 1 below:

$\begin{matrix}{{\rho = \frac{R}{K + {GR}}},} & \left( {{eq}.\mspace{14mu} 2} \right)\end{matrix}$

where the constants K and G are constants. FIG. 17 further shows thatelectrical resistance and electrical resistivity have a linearrelationship for concrete.

K-value Characterization. The electrical resistance R of the concretewas measured using the sensor described herein and the electricalresistivity ρ of the concrete was measured using both digitalresistivity meter and conductivity meter for initial curing period tocalculate the K-value at room temperature. The average K-value forcementitious materials for the prescribed sensor is developed during theinitial curing period, as shown in FIG. 19.

The electrical impedance of concrete at certain ranges of frequencycorrelates to material property, electrical resistivity of concrete.Therefore, according to various embodiments, the electrical propertieshave been well correlated with important early-stage properties ofconcrete such that a variety of properties may be established includingwater cement ratio, insitu compressive strength, initial and finalsetting times, transport property detection, pore solution electricalconductivity, hydration of cementitious materials and damage detection.

Determination of Water to Cement Ratio of Concrete. The measurement ofwater to cement ratio of concrete before or during pouring the concreteis important in the construction industry to ensure the appropriatequality of the concrete delivered by concrete trucks to the constructionsite. Every concrete mix design has a specified water to cement ratio.The water to cement ratio has an impact on the performance of concrete,its hydration, and porosity. Higher water content increases the porosityof the hardened concrete and thus, decreases its strength anddurability. It is important to monitor the water/cement ratio inreal-time. Accordingly, the sensor device 100 described herein helpsavoiding pouring low-strength or low-quality concrete, the replacementof which will be very costly and, in some cases, impossible.

Findings. The electrical resistivity of the concrete slurry was found tovary between 2.5 to 3 Ω-m based on the water content added. For Mix A,the resistivity was 2.9 Ω-m, for Mix B it was 2.60 Ω-m, due to increasedwater to binder ration, as shown in FIG. 20. The resistivity of theflyash concrete varied between 36.13 to 40.5 for percentages Mixes A andB after three days of curing. It was also observed that the resistivityof flyash concrete were lower for higher water to binder ratio. For MixA, the resistivity time factor was 51.7 Ω-m-day and compressive strengthwas 9.1 MPa after one day of curing. The resistivity time factor was354.8 Ω-m-day and 17.2 MPa after two days of curing. After three days ofcuring, the resistivity time factor was 1061.8 MPa and compressivestrength of 21 MPa. Accordingly, it is evident that the water cementratio impact shows correlation to electrical resistivity measurementsduring initial placement of concrete. Such electrical measurements madein the field provide indication of quality of cementitious materialswithout requiring additional testing.

Prediction of In-Situ Compressive Strength of Concrete after Pouring.Assessment of the compressive strength of concrete during the first fewdays from pouring up to sever days after pouring is important for theoptimization of formwork removal, post tensioning, and opening ofroadways especially in the winter. The rate of hydration of everyconcrete mix design differs due to various factors of influence. Theelectrical resistivity of concrete over time can be used to estimate thecompressive strength of concrete, rate of hydration, and calculation ofpercentage of strength gain.

Long term strength prediction may further be employed. Specifically,established resistivity time factor (RTF) versus strength correlationmay be employed to predict the long-term compressive strength ofconcrete. A depiction of the results is presented below.

One-Day Results. The RTF Factor for one day was 33.7 Ω-m-day. Using aprediction curve, the compressive strength was 7±0.5 MPa. The actualone-day strength obtained by performing compressive strength was 7.03MPa, as shown in FIG. 22.

Two-Days Results. The RTF Factor for two days was 286.2 Ω-m-day. Using aprediction curve, the compressive strength was 15.4±0.5 MPa. The actualtwo-day strength obtained by performing compressive strength was 15.3MPa.

Three-Days Results. The RTF Factor for 3 days was 913.3 Ω-m-day. Using aprediction curve, the compressive strength was 19.5±0.5 MPa. The actualone-day strength obtained by performing compressive strength was 19.1MPa. The prediction of compressive strength using resistivity timefactor curve was accurate up to about ±0.5 MPa. Accordingly, it isevident that the compressive strength shows linear correlation toelectrical resistivity and resistivity time factor (RTF) may be utilizedfor prediction of compressive strength without need for break tests.

Initial and Final Setting of Concrete (ASTM C403). Currently, thedetermination of initial and final setting time concrete is performedusing Vicat Apparatus ASTM C403: “Standard Test Method for Time ofSetting of Concrete Mixtures by Penetration Resistance.” This laboratoryprocedure is labor intensive and cannot be employed in the field.Setting times are important for deciding on the surface finishing ofconcrete and for other sequence of operations in the construction.Monitoring the absolute value of electrical resistivity of concreteenables identification of different stages of hydration reaction insideconcrete leading to correlation to setting time of concrete.Accordingly, electrical impedance measurements present a non-invasive,in-site process for detection of setting time of concrete.

Assessment of Transport properties of Concrete. Two important electricalparameters required for reliable and accurate assessment of themicrostructural properties of concrete are electrical conductivity ofbulk concrete and its pore solution. The measurement of these twoproperties also enables calculation of formation factor for concretematerials over time. One of the major drawbacks of current availabletechniques is the inability to monitor these electrical properties ofconcrete materials on the field and in real time for long term. Themeasurement of bulk electrical conductivity of concrete has beendemonstrated. Monitoring the electrical conductivity in real timeenables determination of transport properties of concrete. Accordingly,this assessment can substitute Standards such as ASTM C1202: “StandardTest Method for Electrical Indication of Concrete's Ability to ResistChloride Ion Penetration” and ASTM C1543: “Standard Test Method forDetermining the Penetration of Chloride Ion into Concrete by Ponding.”

Within the embodiments of the invention described, the electrical andtemperature measurements may be made using disposable and/or reusableprobes connected to sensor via a 4 pin waterproof electrical connector.For example, a disposable sensor may exploit Bluetooth connectivity forshort range low power communications and ad-hoc, LORA or other networkprotocols to communicate electrical measurement data to a node or nodeswherein it is pushed to remote servers, what is commonly referred totoday as “the cloud, through one or more different network interfacesand/or network protocols. Subsequently, this cloud stored data can beanalyzed in real time and/or periodically to determine one or more ofthe measurements described.

In addition to measuring, for example, temperature, AC electricalresistivity, and AC electrical conductivity of pore solution, it wouldbe evident that additional parameters as discussed and described inrespect of embodiments of the invention may be measured and monitored,including, but not limited to, concrete moisture content, concreteinternal relative humidity, concrete pH, concrete mixture consistency,concrete workability (slump), and concrete air content.

Accordingly, based on the foregoing, a method for performing real-timeconcrete monitoring is described that includes providing at least onesensor device 100 (e.g., one or more of the sensor device 100 describedabove). The sensor device 100 includes an enclosure 103 configured tocouple the sensor to a concrete reinforcing structure 172, the enclosurecomprising a temperature probe 118, impedance measurement circuitry 136,temperature sensor circuitry 139, and a transceiver module 142. Thesensor device 100 further includes an electrical conducting wire 106extending out from the enclosure 106 being electrically and/orcommunicatively connected to at least one probe 109. The processingcircuitry 127 may be configured to perform at least one impedancemeasurement using the at least one probe 109 and a temperaturemeasurement using the temperature probe 109; and communicate at leastone of the at least one impedance measurement, the at least onetemperature measurement, and derivative information associatedtherewith, to a computing device 175 via the transceiver 142. The methodfurther includes affixing the enclosure 103 of the at least one sensor100 to the concrete reinforcing structure 172; pouring concrete or othermaterial in an area such that the at least one sensor 100 is wholly orpartially encapsulated in the concrete such that the at least one probe109 is in contact with the concrete; receiving, by at least onecomputing device 175, at least one of the at least one impedancemeasurement, the at least one temperature measurement, and derivativeinformation associated therewith from the at least one sensor 100;determining, by the at least one computing device 175, at least one of atemperature, a maturity, a resistivity, and a strength of the concretebased on at least one of: the at least one impedance measurement, the atleast one temperature measurement, and derivative information associatedtherewith; and displaying, by the at least one computing device 175,information associated with at least one of the temperature, thematurity, the resistivity, and the strength of the concrete in a displaydevice.

Additionally, a method is described that includes performing an ACelectrical impedance measurement using a sensor device 100 positionedinside a material comprising at least one of: concrete, cementitiousmaterial, liquid, soil, polymer, and a combination thereof in real-time;and determining a characteristic of the material based upon at least theelectrical impedance measurement, wherein determining the characteristicof the material further comprises adjusting the AC electrical impedancemeasurement based at least in part on an appropriate electrical circuit,geometric factor, and temperature.

In some embodiments, the material includes concrete in one of a wet anda hardened state, and the characteristic of the material is at least oneof the following: a water to cement ratio of the concrete; an estimatedin-situ compressive strength of the concrete after pouring; at least oneof seven-day, twenty-eight-day, and fifty-six-day compressive strengthof the concrete; at least one of the initial and final setting time ofthe concrete; a transport property of the concrete (e.g., permeability,diffusivity, porosity, and any combination thereof); a presence of voidsinside the concrete; a presence of a crack within the concrete; and poresolution characteristics.

The electrical impedance may be obtained using an equivalent circuit, asshown in FIG. 14, and a dependence of geometric factor determined toobtain at least one of electrical resistivity and electricalconductivity to determine the characteristic, where the characteristicmay include a water to cement ratio of the concrete; an in-situcompressive strength of the concrete after pouring; a prediction of atleast one of seven-day, twenty-eight-day, and fifty-six-day compressivestrength of the concrete; a detection of at least one of the initial andfinal setting time of the concrete; and an assessment of a transportproperty of the concrete selected from a group consisting ofpermeability, diffusivity, and porosity.

The features, structures, or characteristics described above may becombined in one or more embodiments in any suitable manner, and thefeatures discussed in the various embodiments are interchangeable, ifpossible. In the following description, numerous specific details areprovided in order to fully understand the embodiments of the presentdisclosure. However, a person skilled in the art will appreciate thatthe technical solution of the present disclosure may be practicedwithout one or more of the specific details, or other methods,components, materials, and the like may be employed. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the presentdisclosure.

Although the relative terms such as “on,” “below,” “upper,” and “lower”are used in the specification to describe the relative relationship ofone component to another component, these terms are used in thisspecification for convenience only, for example, as a direction in anexample shown in the drawings. It should be understood that if thedevice is turned upside down, the “upper” component described above willbecome a “lower” component. When a structure is “on” another structure,it is possible that the structure is integrally formed on anotherstructure, or that the structure is “directly” disposed on anotherstructure, or that the structure is “indirectly” disposed on the otherstructure through other structures.

In this specification, the terms such as “a,” “an,” “the,” and “said”are used to indicate the presence of one or more elements andcomponents. The terms “comprise,” “include,” “have,” “contain,” andtheir variants are used to be open ended, and are meant to includeadditional elements, components, etc., in addition to the listedelements, components, etc. unless otherwise specified in the appendedclaims. The terms “first,” “second,” etc. are used only as labels,rather than a limitation for a number of the objects.

It should be emphasized that the above-described embodiments of thepresent disclosure are merely possible examples of implementations setforth for a clear understanding of the principles of the disclosure.Many variations and modifications may be made to the above-describedembodiment(s) without departing substantially from the spirit andprinciples of the disclosure. All such modifications and variations areintended to be included herein within the scope of this disclosure andprotected by the following claims.

Therefore, the following is claimed:
 1. A sensor device configured to beembedded within concrete and perform real-time monitoring thereof,comprising: an enclosure configured to couple the sensor device to aconcrete reinforcing structure, the enclosure comprising a temperatureprobe, impedance measurement circuitry, temperature sensor circuitry,and a transceiver module; an electrical conducting wire extending outfrom the enclosure being connected to at least one probe; and processingcircuitry configured to: perform at least one impedance measurementusing the at least one probe and a temperature measurement using the atleast one probe; and communicate at least one of the at least oneimpedance measurement, the at least one temperature measurement, andderivative information associated therewith, to a computing device viathe transceiver module.
 2. The sensor device according to claim 1,wherein the concrete reinforcing structure comprises rebar, theenclosure comprising at least one aperture for coupling the enclosure tothe rebar using a connection device, wherein the connection devicecomprises at least one of a zip-tie and a wire-tie.
 3. The sensor deviceaccording to claim 1, wherein: at least one of the processing circuitryand a client application executing on the computing device is furtherconfigured to determine an electrical resistivity of the concrete basedat least in part on the at least one impedance measurement; and theelectrical resistivity is determined based at least in part on apredetermined geometric factor value (K-value) associated with the atleast one probe.
 4. The sensor device according to claim 1, wherein theat least one probe comprises a pair of electrical resistivity andelectrical conductivity probes and a temperature probe.
 5. The sensordevice according to claim 1, wherein: the electrical conducting wire isa first electrical conducting wire; the at least one probe is a part offirst probe arrangement, the first probe arrangement comprising a pairof electrical resistivity and electrical conductivity probes and atemperature probe; the sensor device further comprises a secondelectrical conducting wire; and a second probe arrangement electricallyconnected to the processing circuitry by the second electricalconducting wire.
 6. The sensor device according to claim 5, wherein thesecond probe arrangement comprises a pair of electrodes, a mixing arm,and a filter.
 7. The sensor device according to claim 1, wherein thesensor device is embedded in the concrete.
 8. The sensor deviceaccording to claim 1, wherein the enclosure comprises a temperatureprobe, a bulk material electrical resistivity probe, a pore solutionelectrical conductivity probe, and the processing circuitry.
 9. Thesensor device according to claim 8, the processing circuitry comprises abattery, a microprocessor, impedance measurement circuitry, temperaturemeasurement circuitry, a transceiver, and memory.
 10. The sensor deviceaccording to claim 1, wherein the sensor device is embedded in theconcrete, the concrete being precast concrete, the sensor device furthercomprising a waterproof electrical connector connected to theelectrically conductive water that is positioned partially external tothe precast concrete.
 11. A method for performing real-time concretemonitoring, comprising: providing at least one sensor, the at least onesensor comprising: an enclosure configured to couple the sensor to aconcrete reinforcing structure, the enclosure comprising a temperatureprobe, impedance measurement circuitry, temperature sensor circuitry,and a transceiver module; an electrical conducting wire extending outfrom the enclosure being connected to at least one probe; and processingcircuitry configured to: (a) perform at least one impedance measurementusing the at least one probe and a temperature measurement using thetemperature probe; and (b) communicate at least one of the at least oneimpedance measurement, the at least one temperature measurement, andderivative information associated therewith, to a client device via thetransceiver module; affixing the enclosure of the at least one sensor tothe concrete reinforcing structure; pouring concrete in an area suchthat the at least one sensor is encapsulated in the concrete such thatthe at least one probe is in contact with the concrete; receiving, by atleast one computing device, at least one of the at least one impedancemeasurement, the at least one temperature measurement, and derivativeinformation associated therewith from the at least one sensor;determining, by the at least one computing device, at least one of atemperature, a maturity, a resistivity, and a strength of the concretebased on at least one of: the at least one impedance measurement, the atleast one temperature measurement, and derivative information associatedtherewith; and displaying, by the at least one computing device,information associated with at least one of the temperature, thematurity, the resistivity, and the strength of the concrete in a displaydevice.
 12. A method, comprising: performing an alternating current (AC)electrical impedance measurement using a sensor device positioned insidea material comprising at least one of: concrete, cementitious material,liquid, soil, polymer, and a combination thereof in real-time; anddetermining a characteristic of the material based upon at least theelectrical impedance measurement, wherein determining the characteristicof the material further comprises adjusting the AC electrical impedancemeasurement based at least in part on an appropriate electrical circuit,geometric factor, and temperature.
 13. The method according to claim 12,wherein: the material comprises concrete in one of a wet and a hardenedstate; the characteristic of the material is at least one of thefollowing: determination of the water to cement ratio of the concrete;estimation of in-situ compressive strength of the concrete afterpouring; prediction of at least one of seven-day, twenty-eight-day andfifty-six-day compressive strength of the concrete; detection of atleast one of the initial and final setting time of the concrete;assessment of a transport property of the concrete selected from a groupconsisting of permeability, diffusivity, and porosity; a presence ofvoids inside the concrete; a presence of a crack within the concrete;and determination of pore solution characteristics.
 14. The methodaccording to claim 12, wherein the electrical impedance is obtainedusing an equivalent circuit and a dependence of geometric factordetermined to obtain at least one of electrical resistivity andelectrical conductivity to determine the characteristic.
 15. The methodaccording to claim 14, wherein the characteristic comprises a water tocement ratio of the concrete; an in-situ compressive strength of theconcrete after pouring; a prediction of at least one of seven-day,twenty-eight-day, and fifty-six-day compressive strength of theconcrete; a detection of at least one of the initial and final settingtime of the concrete; and an assessment of a transport property of theconcrete selected from a group consisting of permeability, diffusivity,and porosity.